The IKK-related kinases: from innate immunity to oncogenesis

Black carp A20 inhibits interferon signaling through de-ubiquitinating IKKβ

IkappaB kinase beta (IKKβ) is a key member of IκB kinases and functions importantly in interferon (IFN) signaling. Phosphorylation and ubiquitination are involved in the activation of IKKβ. A20 is a de-ubiquitin enzyme and functions as a suppressor in inflammation signaling, which has been reported to be phosphorylated and activated by IKKβ. However, the role and relationship of IKKβ and A20 in teleost remains unclear. In this study, IKKβ (bcIKKβ) and A20 (bcA20) of black carp (Mylopharyngodon piceus) have been cloned and characterized. Overexpressed bcIKKβ in EPC cells showed strong anti-viral ability by activating both NF-κB and IFN signaling. EPC cells stable expressing bcIKKβ presented improved anti-viral activity as well. The interaction between bcA20 and bcIKKβ was identified, and overexpression of bcA20 was able to suppress bcIKKβ-mediated activation of NF-κB and IFN signaling. Meanwhile, knock-down of A20 increased host the antiviral ability of host cells. Importantly, it has been identified that bcA20 was able to remove K27-linked ubiquitination and decrease the phosphorylation of bcIKKβ. Thus, our data conclude that bcA20 suppresses the anti-viral activity of bcIKKβ and removes its K27-linked ubiquitination, which presents a new mechanism of IKKβ regulation.

Lunar-linked biological rhythms in the immune system of freshwater three-spined stickleback

Immune responses are widely accepted to be under circadian regulation via a molecular clock, with many practical consequences, but much less is known of how other biological rhythms could affect the immune system. In this study, we search for lunar rhythms (circalunar, circasemilunar, and circatidal cycles) in the immune expression of the recently marine-derived freshwater fish, the low-plate morph of the three-spined stickleback. We employed time series of immune expression (mRNA) measurements for 14 immune-associated genes, representing a variety of immunological pathways. Times series measurements were taken on fish populations in the wild, in seminatural outdoor mesocosms, and in the laboratory, according to sampling regimens originally designed to study circannual variation but with the additional potential to provide information about lunar variation. Our evidence best supported the existence of a very small endogenous tidal rhythm. This is consistent with previous suggestions of the existence of a primordial tidal endogenous clock, some elements of which may be conserved in animals evolving outside the marine environment.

High-throughput identification of functional regulatory SNPs in systemic lupus erythematosus

Genome-wide association studies implicate multiple loci in risk for systemic lupus erythematosus (SLE), but few contain exonic variants, rendering systematic identification of non-coding variants essential to decoding SLE genetics. We utilized SNP-seq and bioinformatic enrichment to interrogate 2180 single-nucleotide polymorphisms (SNPs) from 87 SLE risk loci for potential binding of transcription factors and related proteins from B cells. 52 SNPs that passed initial screening were tested by electrophoretic mobility shift and luciferase reporter assays. To validate the approach, we studied rs2297550 in detail, finding that the risk allele enhanced binding to the transcription factor Ikaros (IKZF1), thereby modulating expression of IKBKE. Correspondingly, primary cells from genotyped healthy donors bearing the risk allele expressed higher levels of the interferon / NF-κB regulator IKKϵ. Together, these findings define a set of likely functional non-coding lupus risk variants and identify a new regulatory pathway involving rs2297550, Ikaros, and IKKϵ implicated by human genetics in risk for SLE.

TANK Binding Kinase 1 Promotes BACH1 Degradation through Both Phosphorylation-Dependent and -Independent Mechanisms without Relying on Heme and FBXO22

BTB and CNC homology 1 (BACH1) represses the expression of genes involved in the metabolism of iron, heme and reactive oxygen species. While BACH1 is rapidly degraded when it is bound to heme, it remains unclear how BACH1 degradation is regulated under other conditions. We found that FBXO22, a ubiquitin ligase previously reported to promote BACH1 degradation, polyubiquitinated BACH1 only in the presence of heme in a highly purified reconstitution assay. In parallel to this regulatory mechanism, TANK binding kinase 1 (TBK1), a protein kinase that activates innate immune response and regulates iron metabolism via ferritinophagy, was found to promote BACH1 degradation when overexpressed in 293T cells. While TBK1 phosphorylated BACH1 at multiple serine and threonine residues, BACH1 degradation was observed with not only the wild-type TBK1 but also catalytically impaired TBK1. The BACH1 degradation in response to catalytically impaired TBK1 was not dependent on FBXO22 but involved both autophagy-lysosome and ubiquitin-proteasome pathways judging from its suppression by using inhibitors of lysosome and proteasome. Chemical inhibition of TBK1 in hepatoma Hepa1 cells showed that TBK1 was not required for the heme-induced BACH1 degradation. Its inhibition in Namalwa B lymphoma cells increased endogenous BACH1 protein. These results suggest that TBK1 promotes BACH1 degradation in parallel to the FBXO22- and heme-dependent pathway, placing BACH1 as a downstream effector of TBK1 in iron metabolism or innate immune response.

SUMOylation-Driven mRNA Circularization Enhances Translation and Promotes Lymphatic Metastasis of Bladder Cancer

Aberrant gene expression is a prominent feature of metastatic cancer. Translational initiation is a vital step in fine-tuning gene expression. Thus, exploring translation initiation regulators may identify therapeutic targets for preventing and treating metastasis. Herein, we identified that DHCR24 was overexpressed in lymph node (LN) metastatic bladder cancer and correlated with poor prognosis of patients. DHCR24 promoted lymphangiogenesis and LN metastasis of bladder cancer in vitro and in vivo. Mechanistically, DHCR24 mediated and recognized the SUMO2 modification at lysine 108 of hnRNPA2B1 to foster TBK1 mRNA circularization and eIF4F initiation complex assembly by enhancing hnRNPA2B1-eIF4G1 interaction. Moreover, DHCR24 directly anchored to TBK1 mRNA 3'-untranslated region to increase its stability, thus forming a feed forward loop to elevate TBK1 expression. TBK1 activated PI3K/Akt signaling to promote VEGFC secretion, resulting in lymphangiogenesis and LN metastasis. DHCR24 silencing significantly impeded bladder cancer lymphangiogenesis and lymphatic metastasis in a patient-derived xenograft model. Collectively, these findings elucidate DHCR24-mediated translation machinery that promotes lymphatic metastasis of bladder cancer and supports the potential application of DHCR24-targeted therapy for LN-metastatic bladder cancer.

SIGNIFICANCE

DHCR24 is a SUMOylation regulator that controls translation initiation complex assembly and orchestrates TBK1 mRNA circularization to activate Akt/VEGFC signaling, which stimulates lymphangiogenesis and promotes lymph node metastasis in bladder cancer.

Role of cGAS-STING in colorectal cancer: A new window for treatment strategies

Colorectal cancer (CRC) is a common and deadly form of cancer, leading to the need for new therapeutic targets and strategies for treatment. Recent studies have shown the cGAS-STING pathway to be a promising target for cancer therapy. The cGAS-STING pathway is a part of the innate immune system and serves to identify DNA damage and viral infection, promoting an immune response. Activation of this pathway leads to the production of immune mediators, such as type I interferons, that activate immune cells to attack cancer cells. Research has identified the cGAS-STING pathway as a frequently dysregulated component in CRC, promoting tumor growth and metastasis, or leading to chronic inflammation and tissue damage. The modulation of this pathway presents a potential therapeutic approach, either activating or inhibiting the pathway to enhance the immune response and prevent inflammation, respectively. Developing drugs that can modulate the cGAS-STING pathway offers promise for improving treatment outcomes for CRC patients. The present review explores recent research on the role of cGAS-STING in CRC and highlights the potential therapeutic benefits of targeting this pathway.

An IKBKE variant conferring functional cGAS/STING pathway deficiency and susceptibility to recurrent HSV-2 meningitis

The mechanisms underlying susceptibility to recurrent herpes simplex virus type 2 (HSV-2) meningitis remain incompletely understood. In a patient experiencing multiple episodes of HSV-2 meningitis, we identified a monoallelic variant in the IKBKE gene, which encodes the IKKε kinase involved in induction of antiviral IFN genes. Patient cells displayed impaired induction of IFN-β1 (IFNB1) expression upon infection with HSV-2 or stimulation with double-stranded DNA (dsDNA) and failed to induce phosphorylation of STING, an activation marker of the DNA-sensing cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) pathway. The patient allele encoded a truncated IKKε protein with loss of kinase activity and also capable of exerting dominant-negative activity. In stem cell-derived microglia, HSV-2-induced expression of IFNB1 was dependent on cGAS, TANK binding kinase 1 (TBK1), and IKBKE, but not TLR3, and supernatants from HSV-2-treated microglia exerted IKBKE-dependent type I IFN-mediated antiviral activity upon neurons. Reintroducing wild-type IKBKE into patient cells rescued IFNB1 induction following treatment with HSV-2 or dsDNA and restored antiviral activity. Collectively, we identify IKKε to be important for protection against HSV-2 meningitis and suggest a nonredundant role for the cGAS/STING pathway in human antiviral immunity.

TBK1 variants in Chinese patients with amyotrophic lateral sclerosis: Genetic analysis and clinical features

BACKGROUND AND PURPOSE

Haploinsufficiency of TANK-binding kinase 1 (TBK1) loss-of-function (LoF) variants has been shown to be pathogenic in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). However, the genetic spectrum of TBK1 and clinical features of ALS patients with TBK1 variants remain largely unknown in Asians.

METHODS

Genetic analysis was performed on 2011 Chinese ALS patients. Software was used to predict the deleteriousness of missense variants in TBK1. In addition, PubMed, Embase and Web of Science were searched for related literature.

RESULTS

Twenty-six TBK1 variants were identified in 33 of 2011 ALS patients, including six novel LoF variants (0.3%) and 20 rare missense variants, 12 of which were predicted to be deleterious (0.6%). In addition to TBK1 variants, 11 patients had other ALS-related gene variants. Forty-two previous studies found that the frequency of TBK1 variants was 1.81% in ALS/FTD patients. The frequency of TBK1 LoF variants in ALS was 0.5% (Asians 0.4%; Caucasian 0.6%) and that of missense variants was 0.8% (Asians 1.0%; Caucasian 0.8%). ALS patients with TBK1 LoF variants affecting the kinase domain had a significantly younger age of onset than patients carrying LoF variants affecting the coiled coil domains CCD1 and CCD2. FTD has a frequency of 10% in Caucasian ALS patients with TBK1 LoF variants, which was not found in our cohort.

CONCLUSION

Our study expanded the genotypic spectrum of ALS patients with TBK1 variants and found that the clinical manifestations of TBK1 carriers are diverse.

p38MAPK/MK2 signaling stimulates host cells autophagy pathways to restrict Salmonella infection

Autophagy plays an important role in recognizing and protecting cells from invading intracellular pathogens such as Salmonella. In this work, we investigated the role of p38MAPK/MK2 in modulating the host cell susceptibility to Salmonella infection. Inhibition of p38MAPK or MK2 led to a significant increase of bacterial counts in Salmonella infected mouse embryonic fibroblasts (MEFs), as well as in MK2-deficient (Mk2-/-) cells. Furthermore, western blot analysis showed that Mk2-/- cells have lower level of LC3 lipidation, which is the indicator of general autophagy compared to Mk2-rescued cells. In Mk2-/- cells, we also observed lower activated TANK-binding kinase-1 phosphorylation on Ser172 and p62/SQTM1-Ser403 phosphorylation, which are important to promote the translocation of p62 to ubiquitinated microbes and required for efficient autophagy of bacteria. Furthermore, immunofluorescence analysis revealed reduced colocalization of Salmonella with LC3 and p62 in MEFs. Inhibition of autophagy with bafilomycin A1 showed increased bacterial counts in treated cells compared to control cell. Overall, these results indicate that p38MAPK/MK2-mediated protein phosphorylation modulates the host cell susceptibility to Salmonella infection by affecting the autophagy pathways.

Modulating MGMT expression through interfering with cell signaling pathways

Guanine O6-alkylating agents are widely used as first-line chemotherapeutic drugs due to their ability to induce cytotoxic DNA damage. However, a major hurdle in their effectiveness is the emergence of chemoresistance, largely attributed to the DNA repair pathway mediated by O6-methylguanine-DNA methyltransferase (MGMT). MGMT plays an important role in removing the alkyl groups from lethal O6-alkylguanine (O6-AlkylG) adducts formed by chemotherapeutic alkylating agents. By doing so, MGMT enables tumor cells to evade apoptosis and develop drug resistance toward DNA alkylating agents. Although covalent inhibitors of MGMT, such as O6-benzylguanine (O6-BG) and O6-(4-bromothenyl)guanine (O6-4-BTG or lomeguatrib), have been explored in clinical settings, their utility is limited due to severe delayed hematological toxicity observed in most patients when combined with alkylating agents. Therefore, there is an urgent need to identify new targets and unravel the underlying molecular mechanisms and to develop alternative therapeutic strategies that can overcome MGMT-mediated tumor resistance. In this context, the regulation of MGMT expression via interfering the specific cell signaling pathways (e.g., Wnt/β-catenin, NF-κB, Hedgehog, PI3K/AKT/mTOR, JAK/STAT) emerges as a promising strategy for overcoming tumor resistance, and ultimately enhancing the efficacy of DNA alkylating agents in chemotherapy.

Lipid nanoparticles (LNP) induce activation and maturation of antigen presenting cells in young and aged individuals

Herein, we studied the impact of empty LNP (eLNP), component of mRNA-based vaccine, on anti-viral pathways and immune function of cells from young and aged individuals. eLNP induced maturation of monocyte derived dendritic cells (MDDCs). We further show that eLNP upregulated CD40 and induced cytokine production in multiple DC subsets and monocytes. This coincided with phosphorylation of TANK binding kinase 1 (pTBK1) and interferon response factor 7 (pIRF7). In response to eLNP, healthy older adults (>65 yrs) have decreased CD40 expression, and IFN-γ output compared to young adults (<65 yrs). Additionally, cells from older adults have a dysregulated anti-viral signaling response to eLNP stimulation, measured by the defect in type I IFN production, and phagocytosis. Overall, our data show function of eLNP in eliciting DC maturation and innate immune signaling pathways that is impaired in older adults resulting in lower immune responses to SARS-CoV-2 mRNA-based vaccines.

The inhibitor of κB kinase β (IKKβ) phosphorylates IκBα twice in a single binding event through a sequential mechanism

Phosphorylation of Inhibitor of κB (IκB) proteins by IκB Kinase β (IKKβ) leads to IκB degradation and subsequent activation of nuclear factor κB transcription factors. Of particular interest is the IKKβ-catalyzed phosphorylation of IκBα residues Ser32 and Ser36 within a conserved destruction box motif. To investigate the catalytic mechanism of IKKβ, we performed pre-steady-state kinetic analysis of the phosphorylation of IκBα protein substrates catalyzed by constitutively active, human IKKβ. Phosphorylation of full-length IκBα catalyzed by IKKβ was characterized by a fast exponential phase followed by a slower linear phase. The maximum observed rate (kp) of IKKβ-catalyzed phosphorylation of IκBα was 0.32 s-1 and the binding affinity of ATP for the IKKβ•IκBα complex (Kd) was 12 μM. Substitution of either Ser32 or Ser36 with Ala, Asp, or Cys reduced the amplitude of the exponential phase by approximately 2-fold. Thus, the exponential phase was attributed to phosphorylation of IκBα at Ser32 and Ser36, whereas the slower linear phase was attributed to phosphorylation of other residues. Interestingly, the exponential rate of phosphorylation of the IκBα(S32D) phosphomimetic amino acid substitution mutant was nearly twice that of WT IκBα and 4-fold faster than any of the other IκBα amino acid substitution mutants, suggesting that phosphorylation of Ser32 increases the phosphorylation rate of Ser36. These conclusions were supported by parallel experiments using GST-IκBα(1-54) fusion protein substrates bearing the first 54 residues of IκBα. Our data suggest a model wherein, IKKβ phosphorylates IκBα at Ser32 followed by Ser36 within a single binding event.

Diverse roles of heterogeneous nuclear ribonucleoproteins in viral life cycle

Understanding the host-virus interactions helps to decipher the viral replication strategies and pathogenesis. Viruses have limited genetic content and rely significantly on their host cell to establish a successful infection. Viruses depend on the host for a broad spectrum of cellular RNA-binding proteins (RBPs) throughout their life cycle. One of the major RBP families is the heterogeneous nuclear ribonucleoproteins (hnRNPs) family. hnRNPs are typically localized in the nucleus, where they are forming complexes with pre-mRNAs and contribute to many aspects of nucleic acid metabolism. hnRNPs contain RNA binding motifs and frequently function as RNA chaperones involved in pre-mRNA processing, RNA splicing, and export. Many hnRNPs shuttle between the nucleus and the cytoplasm and influence cytoplasmic processes such as mRNA stability, localization, and translation. The interactions between the hnRNPs and viral components are well-known. They are critical for processing viral nucleic acids and proteins and, therefore, impact the success of the viral infection. This review discusses the molecular mechanisms by which hnRNPs interact with and regulate each stage of the viral life cycle, such as replication, splicing, translation, and assembly of virus progeny. In addition, we expand on the role of hnRNPs in the antiviral response and as potential targets for antiviral drug research and development.

Lipid nanoparticles (LNP) induce activation and maturation of antigen presenting cells in young and aged individuals

Despite the overwhelming success of mRNA-based vaccine in protecting against SARS-CoV-2 infection and reducing disease severity and hospitalization, little is known about the role lipid nanoparticles (LNP) play in initiating immune response. In this report we studied the adjuvantive impact of empty LNP with no mRNA cargo (eLNP) on anti-viral pathways and immune function of cells from young and aged individuals. We found that eLNP induced maturation of monocyte derived dendritic cells by measuring the expression of CD40, CD80, HLA-DR and production of cytokines including IFN-α,IL-6, IFN-γ, IL-12, and IL-21. Flow cytometry analysis of specific dendritic cell subsets showed that eLNP can induce CD40 expression and cytokine production in cDC1, cDC2 and monocytes. Empty LNP (eLNP) effects on dendritic cells and monocytes coincided with induction pIRF7 and pTBK1, which are both important in mitigating innate immune signaling. Interestingly our data show that in response to eLNP stimulus at 6 and 24 hrs, aged individuals have decreased CD40 expression and reduced IFN- γ output compared to young adults. Furthermore, we show that cDC1, cDC2, and CD14 ^dim CD16 ⁺ monocytes from healthy aged individuals have dysregulated anti-viral signaling response to eLNP stimulation as measured by the defect in type I IFN production, phosphorylation of IRF7, TBK-1, and immune function like phagocytosis. These data showed a novel function of eLNP in eliciting DC maturation and innate immune signaling pathways and that some of these functions are impaired in older individuals providing some suggestion of why older individuals (> 65 yrs of age) respond display lower immune responses and adverse events to SARS-CoV-2 mRNA-based vaccines.

CD24 Expression Dampens the Basal Antiviral State in Human Neuroblastoma Cells and Enhances Permissivity to Zika Virus Infection

Zika virus (ZIKV) exhibits distinct selectivity for infection of various cells and tissues, but how host cellular factors modulate varying permissivity remains largely unknown. Previous studies showed that the neuroblastoma cell line SK-N-AS (expressing low levels of cellular protein CD24) was highly restricted for ZIKV infection, and that this restriction was relieved by ectopic expression of CD24. We tested the hypothesis that CD24 expression allowed ZIKV replication by suppression of the antiviral response. SK-N-AS cells expressing an empty vector (termed CD24-low cells) showed elevated basal levels of phosphorylated STAT1, IRF-1, IKKE, and NFκB. In response to exogenously added type I interferon (IFN-I), CD24-low cells had higher-level induction of antiviral genes and activity against two IFN-I-sensitive viruses (VSV and PIV5-P/V) compared to SK-N-AS cells with ectopic CD24 expression (termed CD24-high cells). Media-transfer experiments showed that the inherent antiviral state of CD24-low cells was not dependent on a secreted factor such as IFN-I. Transcriptomics analysis revealed that CD24 expression decreased expression of genes involved in intracellular antiviral pathways, including IFN-I, NFκB, and Ras. Our findings that CD24 expression in neuroblastoma cells represses intracellular antiviral pathways support the proposal that CD24 may represent a novel biomarker in cancer cells for susceptibility to oncolytic viruses.

BACH1 Expression Is Promoted by Tank Binding Kinase 1 (TBK1) in Pancreatic Cancer Cells to Increase Iron and Reduce the Expression of E-Cadherin

BTB and CNC homology 1 (BACH1) represses the expression of genes involved in the metabolism of iron, heme and reactive oxygen species and promotes metastasis of various cancers including pancreatic ductal adenocarcinoma (PDAC). However, it is not clear how BACH1 is regulated in PDAC cells. Knockdown of Tank binding kinase 1 (TBK1) led to reductions of BACH1 mRNA and protein amounts in AsPC−1 human PDAC cells. Gene expression analysis of PDAC cells with knockdown of TBK1 or BACH1 suggested the involvement of TBK1 and BACH1 in the regulation of iron homeostasis. Ferritin mRNA and proteins were both increased upon BACH1 knockdown in AsPC−1 cells. Flow cytometry analysis showed that AsPC−1 cells with BACH1 knockout or knockdown contained lower labile iron than control cells, suggesting that BACH1 increased labile iron by repressing the expression of ferritin genes. We further found that the expression of E-cadherin was upregulated upon the chelation of intracellular iron content. These results suggest that the TBK1-BACH1 pathway promotes cancer cell metastasis by increasing labile iron within cells.

Role of IKKε in the Metabolic Diseases: Physiology, Pathophysiology, and Pharmacology

IKKε (inhibitor of nuclear factor kappa-B kinase ε) is a member of the noncanonical NF-κB pathway. It participates in the inflammatory response and innate immunity against bacteria. In recent decades, IKKε has been closely associated with metabolic regulation. Inhibition of the IKKε pathway can improve fat deposition in the liver, reduce subcutaneous fat inflammation, and improve liver gluconeogenesis in obesity. IKKε is expected to be a new therapeutic target for metabolic diseases such as nonalcoholic fatty liver disease, diabetes, and obesity. Herein, we summarize the structural characterization, physiological function, and pathological role of IKKε in metabolic diseases and small molecule inhibitors of IKKε.

The role of TBK1 in cancer pathogenesis and anticancer immunity

The TANK-binding kinase 1 (TBK1) is a serine/threonine kinase belonging to the non-canonical inhibitor of nuclear factor-κB (IκB) kinase (IKK) family. TBK1 can be activated by pathogen-associated molecular patterns (PAMPs), inflammatory cytokines, and oncogenic kinases, including activated K-RAS/N-RAS mutants. TBK1 primarily mediates IRF3/7 activation and NF-κB signaling to regulate inflammatory cytokine production and the activation of innate immunity. TBK1 is also involved in the regulation of several other cellular activities, including autophagy, mitochondrial metabolism, and cellular proliferation. Although TBK1 mutations have not been reported in human cancers, aberrant TBK1 activation has been implicated in the oncogenesis of several types of cancer, including leukemia and solid tumors with KRAS-activating mutations. As such, TBK1 has been proposed to be a feasible target for pharmacological treatment of these types of cancer. Studies suggest that TBK1 inhibition suppresses cancer development not only by directly suppressing the proliferation and survival of cancer cells but also by activating antitumor T-cell immunity. Several small molecule inhibitors of TBK1 have been identified and interrogated. However, to this point, only momelotinib (MMB)/CYT387 has been evaluated as a cancer therapy in clinical trials, while amlexanox (AMX) has been evaluated clinically for treatment of type II diabetes, nonalcoholic fatty liver disease, and obesity. In this review, we summarize advances in research into TBK1 signaling pathways and regulation, as well as recent studies on TBK1 in cancer pathogenesis. We also discuss the potential molecular mechanisms of targeting TBK1 for cancer treatment. We hope that our effort can help to stimulate the development of novel strategies for targeting TBK1 signaling in future approaches to cancer therapy.

Regulation of IRF3 activation in Human Antiviral Signalling Pathways

The interferon regulatory factor (IRF) family of transcription factors play a vital role in the human innate antiviral immune responses with production of interferons (IFNs) as a hallmark outcome of activation. In recent years, IRF3 has been considered a principal early regulator of type I IFNs (TI-IFNs) directly downstream of intracellular virus sensing. Despite decades of research on IRF-activating pathways, many questions remain on the regulation of IRF3 activation. The kinases IκB kinase epsilon (IKKε) and TANK-binding kinase-1 (TBK1) and the scaffold proteins TRAF family member-associated NF-kappa-B activator (TANK), NF-kappa-B-activating kinase-associated protein 1 (NAP1) and TANK-binding kinase 1-binding protein 1 (TBKBP1)/similar to NAP1 TBK1 adaptor (SINTBAD) are believed to be core components of an IRF3-activation complex yet their contextual involvement and complex composition are still unclear. This review will give an overview of antiviral signaling pathways leading to the activation of IRF3 and discuss recent developments in our understanding of its proximal regulation.

Silence of TANK-binding kinase 1 (TBK1) regulates extracellular matrix degradation of chondrocyte in osteoarthritis by janus kinase (JAK)-signal transducer of activators of transcription (STAT) signaling

TANK-binding kinase 1 (TBK1) was previously reported to be critical for the regulation of osteoclast differentiation. However, its function in osteoarthritis (OA) has not yet been determined. This study aims to reveal the role of TBK1 in the extracellular matrix (ECM) degradation in OA. C57BL/6 J mice were subjected to anterior cruciate ligament transection (ACLT) surgery to establish an OA animal model. ATDC5 cells were treated with IL-1β to construct a cell model of OA. Changes in the expression of TBK1 were analyzed by qRT-PCR, Western blotting, and immunohistochemistry. Safranin O-fast green staining, ELISA, and Western blotting were performed to evaluate the ECM degradation. By searching GSE75181 and GSE6119 datasets, TBK1 was found to be highly expressed in the OA model. Its upregulation was also confirmed in ACLT mice and in a cell model of OA. Silencing of TBK1 reduced cartilage degradation, OARSI score, and serum levels of CTX-II and COMP. Silencing of TBK1 attenuated ECM degradation, as ADAMTS-4, MMP3, and MMP13 were downregulated, whilst SOX9, collagen II, and aggrecan were upregulated. Furthermore, TBK1 activates the JAK/STAT signaling pathway. Transfection of cells with the STAT3 overexpression plasmid blocked the beneficial effects of TBK1 silencing. In conclusion, TBK1 is highly expressed in OA. Silencing of TBK1 inhibited ECM degradation.

Targeting TBK1 Attenuates LPS-Induced NLRP3 Inflammasome Activation by Regulating of mTORC1 Pathways in Trophoblasts

Pathological maternal inflammation and abnormal placentation contribute to several pregnancy-related disorders, including preterm birth, intrauterine growth restriction, and preeclampsia. TANK-binding kinase 1 (TBK1), a serine/threonine kinase, has been implicated in the regulation of various physiological processes, including innate immune response, autophagy, and cell growth. However, the relevance of TBK1 in the placental pro-inflammatory environment has not been investigated. In this study, we assessed the effect of TBK1 inhibition on lipopolysaccharide (LPS)-induced NLRP3 inflammasome activation and its underlying mechanisms in human trophoblast cell lines and mouse placenta. TBK1 phosphorylation was upregulated in the trophoblasts and placenta in response to LPS. Pharmacological and genetic inhibition of TBK1 in trophoblasts ameliorated LPS-induced NLRP3 inflammasome activation, placental inflammation, and subsequent interleukin (IL)-1 production. Moreover, maternal administration of amlexanox, a TBK1 inhibitor, reversed LPS-induced adverse pregnancy outcomes. Notably, TBK1 inhibition prevented LPS-induced NLRP3 inflammasome activation by targeting the mammalian target of rapamycin complex 1 (mTORC1). Thus, this study provides evidence for the biological significance of TBK1 in placental inflammation, suggesting that amlexanox may be a potential therapeutic candidate for treating inflammation-associated pregnancy-related complications.

The innate immune kinase TBK1 directly increases mTORC2 activity and downstream signaling to Akt

TBK1 responds to microbes to initiate cellular responses critical for host innate immune defense. We found previously that TBK1 phosphorylates mTOR (mechanistic target of rapamycin) on S2159 to increase mTOR complex 1 (mTORC1) signaling in response to the growth factor EGF and the viral dsRNA mimetic poly(I:C). mTORC1 and the less well studied mTORC2 respond to diverse cues to control cellular metabolism, proliferation, and survival. Although TBK1 has been linked to Akt phosphorylation, a direct relationship between TBK1 and mTORC2, an Akt kinase, has not been described. By studying MEFs lacking TBK1, as well as MEFs, macrophages, and mice bearing an Mtor S2159A knock-in allele (MtorA/A) using in vitro kinase assays and cell-based approaches, we demonstrate here that TBK1 activates mTOR complex 2 (mTORC2) directly to increase Akt phosphorylation. We find that TBK1 and mTOR S2159 phosphorylation promotes mTOR-dependent phosphorylation of Akt in response to several growth factors and poly(I:C). Mechanistically, TBK1 coimmunoprecipitates with mTORC2 and phosphorylates mTOR S2159 within mTORC2 in cells. Kinase assays demonstrate that TBK1 and mTOR S2159 phosphorylation increase mTORC2 intrinsic catalytic activity. Growth factors failed to activate TBK1 or increase mTOR S2159 phosphorylation in MEFs. Thus, basal TBK1 activity cooperates with growth factors in parallel to increase mTORC2 (and mTORC1) signaling. Collectively, these results reveal cross talk between TBK1 and mTOR, key regulatory nodes within two major signaling networks. As TBK1 and mTOR contribute to tumorigenesis and metabolic disorders, these kinases may work together in a direct manner in a variety of physiological and pathological settings.

A review on the role of TANK-binding kinase 1 signaling in cancer

TANK-binding kinase 1 (TBK1) regulates various biological processes including, NF-κB signaling, immune response, autophagy, cell division, Ras-mediated oncogenesis, and AKT pro-survival signaling. Enhanced TBK1 activity is associated with autoimmune diseases and cancer, suggesting its role in therapeutic targeting of interferonopathies. In addition, dysregulation of TBK1 activity promotes several inflammatory disorders and oncogenesis. Structural and biochemical study reports provide the molecular process of TBK1 activation and recap the substrate selection about TBK1. This review summarizes recent findings on the molecular mechanisms by which TBK1 is involved in cancer signaling. The IKK-ε and TBK1 are together associated with inflammatory diseases by inducing type I IFNs. Furthermore, TBK1 signaling regulates radiation-induced epithelial-mesenchymal transition by controlling phosphorylation of GSK-3β and expression of Zinc finger E-box-binding homeobox 1, suggesting, TBK1 could be targeted for radiotherapy-induced metastasis therapy. Despite a considerable increase in the list of TBK1 inhibitors, only a few has potential to control cancer. Among them, a compound BX795 is considered a potent and selective inhibitor of TBK1. We discussed the therapeutic potential of small-molecule inhibitors of TBK1, particularly those with high selectivity, which will enable further exploration in the therapeutic management of cancer and inflammatory diseases.

The Aging of Adipocytes Increases Expression of Pro-Inflammatory Cytokines Chronologically

Adipose tissue is a significant producer of pro-inflammatory cytokines in obese and old individuals. However, there is no direct evidence of whether and how aged adipocytes enhance the production of pro-inflammatory markers. We aimed to investigate whether the aging adipocytes increase pro-inflammatory markers. Swiss mouse embryonic-tissue-derived 3T3-L1 cells were differentiated into adipocytes and maintained for 60 days in the conditioned medium or 35 days in the unconditioned medium. Additionally, 20-month-old male C57BL/6 mice were fed a standard chow diet for 37 weeks until they were extremely aged, when ~75% of mice died because of aging. Accumulated lipids, pro-inflammatory markers, and nuclear factor kappa B (NF-κB) pathway markers from differentiated adipocytes were analyzed. Pro-inflammatory markers and NF-κB pathway markers of epididymal white adipose tissues (EWATs) and adipocytes from EWATs were also analyzed. We found that the aging adipocytes chronologically accumulated lipids and increased pro-inflammatory markers interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factor-alpha (TNF-α); at the same time, NF-κB p50 markers were also increased while IκBα protein was decreased significantly in conditioned medium. Similar results were observed when differentiated adipocytes were maintained in the unconditioned medium and the adipocytes from EWATs of aged mice. We demonstrated that aging augmented chronic inflammation through the NF-κB signaling pathway in adipocytes and adipose tissue.

Potential role of IFN-α in COVID-19 patients and its underlying treatment options

The coronavirus disease (COVID-19) caused by a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread rapidly worldwide. Given that this contagious viral outbreak is still unfolding, it is urgent to understand the pathogenesis of SARS-CoV-2 infection and explore effective treatments to protect patients from developing a severe illness related to COVID-19. Recently, IFN-α has been considered a potential therapeutic strategy to treat COVID-19 disease, mainly because the innate immune system rapidly produces IFN-α as the first line of defense to combat viral infections. However, IFN-α can also play a role in immunoregulatory effects, causing pathogenic damage and uncontrolled inflammatory responses. There are 13 human IFN-α subtypes that bind to the same receptor and induce different interferon-stimulated gene (ISG) expression, regulating various antiviral and immunoregulatory effects. The varying degrees of inflammatory regulations may raise concerns about the possible side effects to enlarge the inflammatory responses, exacerbating the severity of infection. Thus, the analysis of various IFN-α subtype induction during SARS-CoV-2 infection is necessary in exploring the mechanism of COVID-19 pathogenesis. This review summarizes the current understanding of IFN-α in the pathogenesis of respiratory virus diseases and IFN-α based clinical intervention used in SARS-CoV-2 infection and other respiratory virus diseases. Besides, new ideas in selecting suitable IFN-α subtypes or combinations as drug candidates for viral infection treatment will also be discussed.Key Points• IFN-α plays an important role in anti-viral and immunoregulatory effects in COVID-19 patients caused by SARS-CoV-2.• The uncontrolled inflammation and disease severity correlated to the diversity of IFN-α subtype induction.• Selecting suitable IFN-α subtypes or combinations as drug candidates will be beneficial for the treatment of patients with COVID-19.

DDAH2 suppresses RLR-MAVS-mediated innate antiviral immunity by stimulating nitric oxide-activated, Drp1-induced mitochondrial fission

The RIG-I-like receptor (RLR) signaling pathway is pivotal for innate immunity against invading viruses, and dysregulation of this molecular cascade has been linked to various diseases. Here, we identified dimethylarginine dimethylaminohydrolase 2 (DDAH2) as a potent regulator of the RLR-mediated antiviral response in human and mouse. Overexpression of DDAH2 attenuated RLR signaling, whereas loss of DDAH2 function enhanced RLR signaling and suppressed viral replication ex vivo and in mice. Upon viral infection, DDAH2 relocated to mitochondria, where it induced the production of nitric oxide (NO) and the activation of dynamin-related protein 1 (Drp1), which promoted mitochondrial fission and blocked the activation of innate immune responses mediated by mitochondrial antiviral signaling (MAVS). TANK-binding kinase 1 (TBK1), a kinase downstream of MAVS, inhibited DDAH2 by phosphorylating DDAH2 at multiple sites. Our study thus identifies a reciprocal inhibitory loop between the DDAH2-NO cascade and the RLR signaling pathway that fine-tunes the antiviral immune response.

Amyotrophic Lateral Sclerosis and Frontotemporal Lobar Degenerations: Similarities in Genetic Background

Amyotrophic lateral sclerosis (ALS) is a devastating, uniformly lethal progressive degenerative disorder of motor neurons that overlaps with frontotemporal lobar degeneration (FTLD) clinically, morphologically, and genetically. Although many distinct mutations in various genes are known to cause amyotrophic lateral sclerosis, it remains poorly understood how they selectively impact motor neuron biology and whether they converge on common pathways to cause neuronal degeneration. Many of the gene mutations are in proteins that share similar functions. They can be grouped into those associated with cell axon dynamics and those associated with cellular phagocytic machinery, namely protein aggregation and metabolism, apoptosis, and intracellular nucleic acid transport. Analysis of pathways implicated by mutant ALS genes has provided new insights into the pathogenesis of both familial forms of ALS (fALS) and sporadic forms (sALS), although, regrettably, this has not yet yielded definitive treatments. Many genes play an important role, with TARDBP, SQSTM1, VCP, FUS, TBK1, CHCHD10, and most importantly, C9orf72 being critical genetic players in these neurological disorders. In this mini-review, we will focus on the molecular mechanisms of these two diseases.

The Sp1-Responsive microRNA-15b Negatively Regulates Rhabdovirus-Triggered Innate Immune Responses in Lower Vertebrates by Targeting TBK1

As is known to all, the production of type I interferon (IFN) plays pivotal roles in host innate antiviral immunity, and its moderate production play a positive role in promoting the activation of host innate antiviral immune response. However, the virus will establish a persistent infection model by interfering with the production of IFN, thereby evading the organism inherent antiviral immune response. Therefore, it is of great necessity to research the underlying regulatory mechanisms of type I IFN appropriate production under viral invasion. In this study, we report that a Sp1–responsive miR-15b plays a negative role in siniperca chuatsi rhabdovirus (SCRV)-triggered antiviral response in teleost fish. We found that SCRV could dramatically upregulate miiuy croaker miR-15b expression. Enhanced miR-15b could negatively regulate SCRV-triggered antiviral genes and inflammatory cytokines production by targeting TANK-binding kinase 1 (TBK1), thereby accelerating viral replication. Importantly, we found that miR-15b feedback regulates antiviral innate immune response through NF-κB and IRF3 signaling pathways. These findings highlight that miR-15b plays a crucial role in regulating virus–host interactions, which outlines a new regulation mechanism of fish’s innate immune responses.

TRK-Fused Gene (TFG), a protein involved in protein secretion pathways, is an essential component of the antiviral innate immune response

Antiviral innate immune response to RNA virus infection is supported by Pattern-Recognition Receptors (PRR) including RIG-I-Like Receptors (RLR), which lead to type I interferons (IFNs) and IFN-stimulated genes (ISG) production. Upon sensing of viral RNA, the E3 ubiquitin ligase TNF Receptor-Associated Factor-3 (TRAF3) is recruited along with its substrate TANK-Binding Kinase (TBK1), to MAVS-containing subcellular compartments, including mitochondria, peroxisomes, and the mitochondria-associated endoplasmic reticulum membrane (MAM). However, the regulation of such events remains largely unresolved. Here, we identify TRK-Fused Gene (TFG), a protein involved in the transport of newly synthesized proteins to the endomembrane system via the Coat Protein complex II (COPII) transport vesicles, as a new TRAF3-interacting protein allowing the efficient recruitment of TRAF3 to MAVS and TBK1 following Sendai virus (SeV) infection. Using siRNA and shRNA approaches, we show that TFG is required for virus-induced TBK1 activation resulting in C-terminal IRF3 phosphorylation and dimerization. We further show that the ability of the TRAF3-TFG complex to engage mTOR following SeV infection allows TBK1 to phosphorylate mTOR on serine 2159, a post-translational modification shown to promote mTORC1 signaling. We demonstrate that the activation of mTORC1 signaling during SeV infection plays a positive role in the expression of Viperin, IRF7 and IFN-induced proteins with tetratricopeptide repeats (IFITs) proteins, and that depleting TFG resulted in a compromised antiviral state. Our study, therefore, identifies TFG as an essential component of the RLR-dependent type I IFN antiviral response.

Antiviral innate immune response is the first line of defence against the invading viruses through type I interferon (IFN) signaling. However, viruses have devised ways to target signaling molecules for aberrant IFN response and worsen the disease outcome. As such, deciphering the roles of new regulators of innate immunity could transform the antiviral treatment paradigm by introducing novel panviral therapeutics designed to reinforce antiviral host responses. This could be of great use in fighting recent outbreaks of severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome MERS-CoV, and the more recent SARS-CoV-2 causing the COVID-19 pandemic. However, aberrant activation of such pathways can lead to detrimental consequences, including autoimmune diseases. Regulation of type I IFN responses is thus of paramount importance. To prevent an uncontrolled response, signaling events happen in discrete subcellular compartments, therefore, distinguishing sites involved in recognition of pathogens and those permitting downstream signaling. Here, we show TFG as a new regulator of type I IFN response allowing the efficient organization of signaling molecules. TFG, thus, further substantiates the importance of the protein trafficking machinery in the regulation of optimal antiviral responses. Our findings have implications for both antiviral immunity and autoimmune diseases.

TBK1 regulates regeneration of pancreatic β-cells

Small-molecule inhibitors of non-canonical IκB kinases TANK-binding kinase 1 (TBK1) and IκB kinase ε (IKKε) have shown to stimulate β-cell regeneration in multiple species. Here we demonstrate that TBK1 is predominantly expressed in β-cells in mammalian islets. Proteomic and transcriptome analyses revealed that genetic silencing of TBK1 increased expression of proteins and genes essential for cell proliferation in INS-1 832/13 rat β-cells. Conversely, TBK1 overexpression decreased sensitivity of β-cells to the elevation of cyclic AMP (cAMP) levels and reduced proliferation of β-cells in a manner dependent on the activity of cAMP-hydrolyzing phosphodiesterase 3 (PDE3). While the mitogenic effect of (E)3-(3-phenylbenzo[c]isoxazol-5-yl)acrylic acid (PIAA) is derived from inhibition of TBK1, PIAA augmented glucose-stimulated insulin secretion (GSIS) and expression of β-cell differentiation and proliferation markers in human embryonic stem cell (hESC)-derived β-cells and human islets. TBK1 expression was increased in β-cells upon diabetogenic insults, including in human type 2 diabetic islets. PIAA enhanced expression of cell cycle control molecules and β-cell differentiation markers upon diabetogenic challenges, and accelerated restoration of functional β-cells in streptozotocin (STZ)-induced diabetic mice. Altogether, these data suggest the critical function of TBK1 as a β-cell autonomous replication barrier and present PIAA as a valid therapeutic strategy augmenting functional β-cells.

Anti-virus effects of interferon regulatory factors (IRFs) identified in ascidian Ciona savignyi

Interferon regulatory factors (IRFs) are key transcription factors that function in the immune system via the interferon (IFN) pathway. In the current study, we identified and characterized three IRFs (CsIRFL1, CsIRFL2, and CsIRFL3) from ascidian Ciona savignyi. Phylogenetic analysis showed that CsIRFL1 was clustered with two IRFs from Ciona robusta and shrimp IRF apart from the vertebrate IRFs, whereas CsIRFL2 and CsIRFL3 were grouped with an unnamed protein from Oikopleura dioica into a sub-branch highly identifying with the vertebrate IRF4, IRF8, and IRF9. Gene expression analysis revealed that CsIRFL1 and CsIRFL2 expressed in all the examined adult tissues (stomach, intestines, eggs, hemocytes, gonad, heart, and pharynx) and predominantly in hemocytes. However, the expression of CsIRFL3 was undetectable in the tested adult tissues. Furthermore, in situ hybridization showed that CsIRFL1 and CsIRFL2 mainly expressed in immunocytes within hemolymph, including phagocytes, macrophage-like cells, morula cells, and amoebocytes, suggesting CsIRFL1 and CsIRFL2 were involved in ascidian immune responses. We then performed LPS and poly(I:C) challenge assay and found that CsIRFL1 highly expressed in the cultured hemocytes following LPS infection for 24 h. After viral analogue poly(I:C) stimulation, the expression of CsIRFL2 was dramatically upregulated from 12 to 24 h. Meanwhile, two critical components of the IFN signaling pathways, STAT and TBK1, showed the increased expression as well after poly(I:C) induction, indicating that CsIRFL2 and IFN pathways genes were activated under the infection of viral analogue. Thus, our findings suggested that CsIRFL2 was a potential transcriptional regulatory factor that participated in regulating the ascidian anti-virus immune response.

IκB kinase-ε-mediated phosphorylation triggers IRF-1 degradation in breast cancer cells

Interferon Regulatory Factors (IRFs) are key regulators of immunity, cell survival and apoptosis. IRF transcriptional activity and subcellular localization are tightly regulated by posttranscriptional modifications including phosphorylation. The IκB kinase family member IKK-ε is essential in regulating antiviral innate immunity mediated by IRFs but is now also recognized as an oncoprotein amplified and overexpressed in breast cancer cell lines and patient-derived tumors. In the present study, we report that the tumor suppressor IRF-1 is a specific target of IKK-ε in breast cancer cells. IKK-ε-mediated phosphorylation of IRF-1 dramatically decreases IRF-1 protein stability, accelerating IRF-1 degradation and quenching IRF-1 transcriptional activity. Chemical inhibition of IKK-ε activity, fully restores IRF-1 levels and function and positively correlates with inhibition of cell growth and proliferation of breast cancer cells. By using a breast cancer cell line stably expressing a dominant negative version of IRF-1 we were able to demonstrate that IKK-ε preferentially exerts its oncogenic potential in breast cancer through the regulation of IRF-1 and point to the IKK-ε-mediated phosphorylation of IRF-1 as a therapeutic target to overcome IKK-ε-mediated tumorigenesis.

IKKε deficiency inhibits acute lung injury following renal ischemia reperfusion injury

Renal ischemia reperfusion injury (IRI) after surgery may promote acute lung injury (ALI) by inducing an inflammatory response. However, the underlying molecular mechanism is still unclear. Studies have reported that inhibitor of κB kinase (IKK)ε primarily regulates inflammation and cell proliferation. The present study aimed to investigate the regulatory role of IKKε in ALI in mice, in order to provide an experimental basis for preventing ALI following surgery-induced renal IRI. C57BL/6J wild-type (WT) and IKKε knockout (IKKε^−/−) mice underwent bilateral renal pedicle occlusion. The plasma creatinine concentration, urea nitrogen level and lung wet-to-dry ratio were measured at baseline, and at 24 and 48 h after declamping. The histological localization and protein levels of inflammatory factors, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-10, were analyzed in lung tissues. Subsequently, the interactions between IKKε and components of the nuclear factor (NF)-κB pathway were studied. The results of the present study demonstrated that the IKKε^−/− groups displayed similar renal function but less pulmonary edema compared with that of the WT groups. The levels of proinflammatory factors in the lungs were significantly upregulated in WT mice compared with those in IKKε^−/− mice after IRI surgery. The NF-κB pathway components and downstream factors were substantially upregulated in the WT groups after acute ischemic kidney injury, and these effects were significantly inhibited in the IKKε^−/− groups. Based on these data, the present study hypothesized that IKKε may serve a negative role in kidney-lung crosstalk after renal IRI and may be a novel target for the treatment of patients with renal IRI.

PINK1/Parkin Influences Cell Cycle by Sequestering TBK1 at Damaged Mitochondria, Inhibiting Mitosis

PINK1 and Parkin are established mediators of mitophagy, the selective removal of damaged mitochondria by autophagy. PINK1 and Parkin have been proposed to act as tumor suppressors, as loss-of-function mutations are correlated with enhanced tumorigenesis. However, it is unclear how PINK1 and Parkin act in coordination during mitophagy to influence the cell cycle. Here we show that PINK1 and Parkin genetically interact with proteins involved in cell cycle regulation, and loss of PINK1 and Parkin accelerates cell growth. PINK1- and Parkin-mediated activation of TBK1 at the mitochondria during mitophagy leads to a block in mitosis due to the sequestration of TBK1 from its physiological role at centrosomes during mitosis. Our study supports a diverse role for the far-reaching, regulatory effects of mitochondrial quality control in cellular homeostasis and demonstrates that the PINK1/Parkin pathway genetically interacts with the cell cycle, providing a framework for understanding the molecular basis linking PINK1 and Parkin to mitosis.

Sarraf et al. use mouse and fly genetics to discover that PINK1 and Parkin influence cell cycle progression. Mitophagy and mitosis independently activate TBK1 at damaged mitochondria and centrosomes, respectively, influencing whether the cell will address mitochondrial quality control or progress with proliferation.

The breast cancer oncogene IKKε coordinates mitochondrial function and serine metabolism

IκB kinase ε (IKKε) is a key molecule at the crossroads of inflammation and cancer. Known to regulate cytokine secretion via NFκB and IRF3, the kinase is also a breast cancer oncogene, overexpressed in a variety of tumours. However, to what extent IKKε remodels cellular metabolism is currently unknown. Here, we used metabolic tracer analysis to show that IKKε orchestrates a complex metabolic reprogramming that affects mitochondrial metabolism and consequently serine biosynthesis independently of its canonical signalling role. We found that IKKε upregulates the serine biosynthesis pathway (SBP) indirectly, by limiting glucose‐derived pyruvate utilisation in the TCA cycle, inhibiting oxidative phosphorylation. Inhibition of mitochondrial function induces activating transcription factor 4 (ATF4), which in turn drives upregulation of the expression of SBP genes. Importantly, pharmacological reversal of the IKKε‐induced metabolic phenotype reduces proliferation of breast cancer cells. Finally, we show that in a highly proliferative set of ER negative, basal breast tumours, IKKε and PSAT1 are both overexpressed, corroborating the link between IKKε and the SBP in the clinical context.

The Specific IKKε/TBK1 Inhibitor Amlexanox Suppresses Human Melanoma by the Inhibition of Autophagy, NF-κB and MAP Kinase Pathways

Inhibitor-kappaB kinase epsilon (IKKε) and TANK-binding kinase 1 (TBK1) are non-canonical IκB kinases, both described as contributors to tumor growth and metastasis in different cancer types. Several hints indicate that they are also involved in the pathogenesis of melanoma; however, the impact of their inhibition as a potential therapeutic measure in this "difficult-to-treat" cancer type has not been investigated so far. We assessed IKKε and TBK1 expression in human malignant melanoma cells, primary tumors and the metastasis of melanoma patients. Both kinases were expressed in the primary tumor and in metastasis and showed a significant overexpression in tumor cells in comparison to melanocytes. The pharmacological inhibition of IKKε/TBK1 by the approved drug amlexanox reduced cell proliferation, migration and invasion. Amlexanox did not affect the cell cycle progression nor apoptosis induction but significantly suppressed autophagy in melanoma cells. The analysis of potential functional downstream targets revealed that NF-кB and ERK pathways might be involved in kinase-mediated effects. In an in vivo xenograft model in nude mice, amlexanox treatment significantly reduced tumor growth. In conclusion, amlexanox was able to suppress tumor progression potentially by the inhibition of autophagy as well as NF-кB and MAP kinase pathways and might therefore constitute a promising candidate for melanoma therapy.

SARS-CoV-2 infection-induced immune responses: Friends or foes?

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) is an emerging coronavirus that belongs to the β‐genus, causing the outbreak of coronavirus disease 19 (COVID‐19). SARS‐CoV‐2 infection can stimulate a pronounced immune response in the host, which embodies in the decrease of lymphocytes and aberrant increase of cytokines in COVID‐19 patients. SARS‐CoV‐2 RNA and proteins interact with various pattern recognition receptors that switch on antiviral immune responses to regulate viral replication and spreading within the host in vivo. However, overactive and impaired immune responses also cause immune damage and subsequent tissue inflammation. This article focuses on the dual roles of immune system during SARS‐CoV‐2 infection, providing a theoretical basic for identifying therapeutic targets in a situation with an unfavourable immune reaction.

Whole exome sequencing in unclassified autoinflammatory diseases: more monogenic diseases in the pipeline?

Objective

Autoinflammatory diseases (AIDs) are characterized by recurrent sterile systemic inflammation attacks. More than half of the patients remain genetically undiagnosed with next-generation sequencing panels for common AIDs. In this study, we aimed to define phenotype-genotype correlations in a cohort of unclassified AID patients via whole exome sequencing (WES).

Methods

Patients with features of AIDs were included in this study followed in the Department of Pediatric Rheumatology at Hacettepe University. They were first screened for MEFV with Sanger sequencing and then WES performed for the patients with clinically insignificant results. Pre-analysis of WES data was done by considering the 13 most common AID-related genes. Further bioinformatic analysis was performed if the patient remained genetically undiagnosed.

Results

The median age at disease onset was 1.2 years (range 0.2–16) and at the time of study recruitment was 14 years (range 3.5–17). In our cohort, WES provided a definite or probable disease-causing variant in 4 of 11 patients (36%). Heterozygous mutations for two of these genes were previously associated with neurological defects (ADAM17, TBK1), also homozygous ADAM17 mutations were observed in one family with neonatal inflammatory skin and bowel disease. Besides, two genes (LIG4, RAG1) were associated with immunodeficiency although the patients had presented with inflammatory features. Finally, for one patient, we associated a strong candidate gene (NLRC3) with autoinflammatory features.

Conclusion

WES strategy is cost-effective and provides substantial results for a selected group of undefined AID patients. Our results will contribute to the spectrum of unclassified AIDs.

Roles of GSK-3 and β-Catenin in Antiviral Innate Immune Sensing of Nucleic Acids

The rapid activation of the type I interferon (IFN) antiviral innate immune response relies on ubiquitously expressed RNA and DNA sensors. Once engaged, these nucleotide-sensing receptors use distinct signaling modules for the rapid and robust activation of mitogen-activated protein kinases (MAPKs), the IκB kinase (IKK) complex, and the IKK-related kinases IKKε and TANK-binding kinase 1 (TBK1), leading to the subsequent activation of the activator protein 1 (AP1), nuclear factor-kappa B (NF-κB), and IFN regulatory factor 3 (IRF3) transcription factors, respectively. They, in turn, induce immunomodulatory genes, allowing for a rapid antiviral cellular response. Unlike the MAPKs, the IKK complex and the IKK-related kinases, ubiquitously expressed glycogen synthase kinase 3 (GSK-3) α and β isoforms are active in unstimulated resting cells and are involved in the constitutive turnover of β-catenin, a transcriptional coactivator involved in cell proliferation, differentiation, and lineage commitment. Interestingly, studies have demonstrated the regulatory roles of both GSK-3 and β-catenin in type I IFN antiviral innate immune response, particularly affecting the activation of IRF3. In this review, we summarize current knowledge on the mechanisms by which GSK-3 and β-catenin control the antiviral innate immune response to RNA and DNA virus infections.

Ubiquitin and Receptor-Dependent Mitophagy Pathways and Their Implication in Neurodegeneration

Selective autophagy of mitochondria, or mitophagy, refers to the specific removal and degradation of damaged or surplus mitochondria via targeting to the lysosome for destruction. Disruptions in this homeostatic process may contribute to disease. The identification of diverse mitophagic pathways and how selectivity for each of these pathways is conferred is just beginning to be understood. The removal of both damaged and healthy mitochondria under disease and physiological conditions is controlled by either ubiquitin-dependent or receptor-dependent mechanisms. In this review, we will discuss the known types of mitophagy observed in mammals, recent findings related to PINK1/Parkin-mediated mitophagy (which is the most well-studied form of mitophagy), the implications of defective mitophagy to neurodegenerative processes, and unanswered questions inspiring future research that would enhance our understanding of mitochondrial quality control.

Advances in IKBKE as a potential target for cancer therapy

IKBKE (inhibitor of nuclear factor kappa-B kinase subunit epsilon), a member of the nonclassical IKK family, plays an important role in the regulation of inflammatory reactions, activation and proliferation of immune cells, and metabolic diseases. Recent studies have demonstrated that IKBKE plays a crucial regulatory role in malignant tumor development. In recent years, IKBKE, an important oncoprotein in several kinds of tumors, has been widely found to regulate a variety of cytokines and signaling pathways. IKBKE promotes the growth, proliferation, invasion, and drug resistance of various cancers. This paper makes a detailed review that focuses on the recent discoveries of IKBKE in the malignant tumors, and puts forward that IKBKE is becoming an important therapeutic target for clinical treatment, which has been more and more realized.

IKBKE enhances TMZ-chemoresistance through upregulation of MGMT expression in glioblastoma

PURPOSE

Glioblastoma multiforme (GBM) is the most common and aggressive malignant type of brain tumor. Despite advances in diagnosis and therapy, the prognosis of patients with GBM has remained dismal. Multidrug resistance and high recurrence are two of the major challenges in successfully treating brain tumors. IKBKE (inhibitor of nuclear factor kappa-B kinase subunit epsilon) is a major oncogenic protein in tumors and can inhibit glioblastoma cell proliferation, migration, and tumorigenesis. Our study aimed to investigate the mechanism of IKBKE enhancing the resistance of glioma cells to temozolomide.

METHODS

For the in vitro experiments, LN18 and U118 glioblastoma cells were treated with a combination of sh/oe-IKBKE lentivirus and TMZ. Cell proliferation was determined by the EdU assay and colony formation assays. Apoptosis was analyzed by the TUNEL assay. In vivo, LN18 NC and LN18 sh-IKBKE cells were implanted into the cerebrums of nude mice to detect the effect of combination therapy. The protein and mRNA levels were assayed by western blot, immunohistochemistry, and qRT-PCR.

RESULTS

In this study, we demonstrated that IKBKE enhances the resistance of glioblastoma cells to temozolomide (TMZ) by activating the AKT/NF-κB signaling pathway to upregulate the expression of the DNA repair enzyme o6-methylguanine-dna methyltransferase (MGMT). In glioblastoma cells, IKBKE knockdown enhances apoptosis and suppresses cell proliferation, clone formation, and tumor development in vivo induced by TMZ. However, overexpression of IKBKE reduces the effects of TMZ.

CONCLUSION

Our studies suggest that inhibition of IKBKE can enhance the therapeutic effect of TMZ on GBM in vitro and in vivo, providing new research directions and therapeutic targets for the treatment of GBM.

Amlexanox ameliorates acetaminophen-induced acute liver injury by reducing oxidative stress in mice

Amlexanox, a clinically approved small-molecule therapeutic presently used to treat allergic rhinitis, ulcer, and asthma, is an inhibitor of the noncanonical IkB kinase-ε (IKKε) and TANK-binding kinase 1 (TBK1). This study was to investigate the protective mechanism of amlexanox in acetaminophen (APAP)-induced acute liver injury (ALI). Mice were intraperitoneally injected with APAP (300 mg/kg, 12 h) to induce ALI and were orally administrated with amlexanox (25, 50 and 100 mg/kg) one hour after APAP treatment. Inhibition of IKKε and TBK1 by treatment of amlexanox attenuated APAP-induced ALI as confirmed by decreased serum levels of aspartate aminotransferase and alanine aminotransferase. Furthermore, amlexanox significantly decreased hepatocellular apoptosis in injured livers of mice as evidenced by histopathologic observation. Consistently, reduced oxidative stress by amlexanox was observed by increased hepatic glutathione concomitant with decreased levels of malondialdehyde. Amlexanox also enhanced expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) target genes including heme oxygenase 1, NAD(P)H:quinone oxidoreductase 1, and glutamate-cysteine ligase in injured livers of mice. Mechanistic insights into the mode of action of amlexanox against APAP-induced hepatotoxicity were involved in increasing phosphorylation of AMP-activated protein kinase (AMPK) and nuclear translocation of Nrf2, both in vivo and in vitro. Furthermore, the protective effects of amlexanox on APAP-induced hepatotoxicity were abolished by compound C, an AMPK inhibitor. Taken together, our findings suggest that amlexanox exerts antioxidative activities against APAP-mediated hepatotoxicity via AMPK/Nrf2 pathway.

14-3-3 scaffold proteins mediate the inactivation of trim25 and inhibition of the type I interferon response by herpesvirus deconjugases

The 14-3-3 molecular scaffolds promote type I interferon (IFN) responses by stabilizing the interaction of RIG-I with the TRIM25 ligase. Viruses have evolved unique strategies to halt this cellular response to support their replication and spread. Here, we report that the ubiquitin deconjugase (DUB) encoded in the N-terminus of the Epstein-Barr virus (EBV) large tegument protein BPLF1 harnesses 14-3-3 molecules to promote TRIM25 autoubiquitination and sequestration of the ligase into inactive protein aggregates. Catalytically inactive BPLF1 induced K48-linked autoubiquitination and degradation of TRIM25 while the ligase was mono- or di-ubiquitinated in the presence of the active viral enzyme and formed cytosolic aggregates decorated by the autophagy receptor p62/SQSTM1. Aggregate formation and the inhibition of IFN response were abolished by mutations of solvent exposed residues in helix-2 of BPLF1 that prevented binding to 14-3-3 while preserving both catalytic activity and binding to TRIM25. 14-3-3 interacted with the Coiled-Coil (CC) domain of TRIM25 in in vitro pulldown, while BPLF1 interacted with both the CC and B-box domains, suggesting that 14-3-3 positions BPLF1 at the ends of the CC dimer, close to known autoubiquitination sites. Our findings provide a molecular understanding of the mechanism by which a viral deubiquitinase inhibits the IFN response and emphasize the role of 14-3-3 proteins in modulating antiviral defenses.

Middle East respiratory syndrome coronavirus-encoded ORF8b strongly antagonizes IFN-β promoter activation: its implication for vaccine design

Middle East respiratory syndrome coronavirus (MERS-CoV) is a causative agent of severe-to-fatal pneumonia especially in patients with pre-existing conditions, such as smoking and chronic obstructive pulmonary disease (COPD). MERS-CoV transmission continues to be reported in the Saudi Arabian Peninsula since its discovery in 2012. However, it has rarely been epidemic outside the area except one large outbreak in South Korea in May 2015. The genome of the epidemic MERS-CoV isolated from a Korean patient revealed its homology to previously reported strains. MERS-CoV encodes 5 accessory proteins and generally, they do not participate in the genome transcription and replication but rather are involved in viral evasion of the host innate immune responses. Here we report that ORF8b, an accessory protein of MERS-CoV, strongly inhibits both MDA5- and RIG-I-mediated activation of interferon beta promoter activity while downstream signaling molecules were left largely unaffected. Of note, MDA5 protein levels were significantly down-regulated by ORF8b and co-expression of ORF4a and ORF4b. These novel findings will facilitate elucidation of mechanisms of virus-encoded evasion strategies, thus helping design rationale antiviral countermeasures against deadly MERS-CoV infection.

UBL4A Augments Innate Immunity by Promoting the K63-Linked Ubiquitination of TRAF6

Human UBL4A/GdX, encoding an ubiquitin-like protein, was shown in this study to be upregulated by viral infection and IFN stimulation. Then the functions of UBL4A in antiviral immune response were characterized. Overexpression of UBL4A promoted RNA virus-induced ISRE or IFN-β or NF-κB activation, leading to enhanced type I IFN transcription and reduced virus replication. Consistently, knockdown of UBL4A resulted in reduced type I IFN transcription and enhanced virus replication. Additionally, overexpression of UBL4A promoted virus-induced phosphorylation of TBK1, IRF3, and IKKα/β. Knockdown of UBL4A inhibited virus-induced phosphorylation of TBK1, IRF3, and IKKα/β. Coimmunoprecipitation showed that UBL4A interacted with TRAF6, and this interaction was enhanced upon viral infection. Ubiquitination assays showed that UBL4A promoted the K63-linked ubiquitination of TRAF6. Therefore, we reveal a novel positive feedback regulation of UBL4A in innate immune response combating virus invasion by enhancing the K63-linked ubiquitination of TRAF6.

Targeting Oncogenic Nuclear Factor Kappa B Signaling with Redox-Active Agents for Cancer Treatment

SIGNIFICANCE

Nuclear factor kappa B (NF-κB) signaling is essential under physiologically relevant conditions. However, aberrant activation of this pathway plays a pertinent role in tumorigenesis and contributes to resistance. Recent Advances: The importance of the NF-κB pathway means that its targeting must be specific to avoid side effects. For many currently used therapeutics and those under development, the ability to generate reactive oxygen species (ROS) is a promising strategy.

CRITICAL ISSUES

As cancer cells exhibit greater ROS levels than their normal counterparts, they are more sensitive to additional ROS, which may be a potential therapeutic niche. It is known that ROS are involved in (i) the activation of NF-κB signaling, when in sublethal amounts; and (ii) high levels induce cytotoxicity resulting in apoptosis. Indeed, ROS-induced cytotoxicity is valuable for its capabilities in killing cancer cells, but establishing the potency of ROS for effective inhibition of NF-κB signaling is necessary. Indeed, some cancer treatments, currently used, activate NF-κB and may stimulate oncogenesis and confer resistance.

FUTURE DIRECTIONS

Thus, combinatorial approaches using ROS-generating agents alongside conventional therapeutics may prove an effective tactic to reduce NF-κB activity to kill cancer cells. One strategy is the use of thiosemicarbazones, which form redox-active metal complexes that generate high ROS levels to deliver potent antitumor activity. These agents also upregulate the metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1), which functions as an NF-κB signaling inhibitor. It is proposed that targeting NF-κB signaling may proffer a new therapeutic niche to improve the efficacy of anticancer regimens.

Essential Roles for the Non-Canonical IκB Kinases in Linking Inflammation to Cancer, Obesity, and Diabetes

Non-canonical IκB kinases (IKKs) TBK1 and IKKε have essential roles as regulators of innate immunity and cancer. Recent work has also implicated these kinases in distinctively controlling glucose homeostasis and repressing adaptive thermogenic and mitochondrial biogenic response upon obesity-induced inflammation. Additionally, TBK1 and IKKε regulate pancreatic β-cell regeneration. In this review, we summarize current data on the functions and molecular mechanisms of TBK1 and IKKε in orchestrating inflammation to cancer, obesity, and diabetes.

MiR-19a mediates the negative regulation of the NF-κB pathway in lipopolysaccharide-induced endometritis by targeting TBK1

OBJECTIVE

In both humans and animals, endometritis is severe inflammation of the uterus, and it causes great economic losses in dairy cow production. MicroRNAs have been reported to play an important role in various inflammatory diseases. However, the regulatory mechanisms of miR-19a in endometritis remain unclear. Thus, the aims of this study are to investigate the role of miR-19a in a mouse model of lipopolysaccharide (LPS)-induced endometritis and elucidate the possible mechanisms in bovine endometrial epithelial cells (bEECs).

METHODS AND RESULTS

Histological analysis showed that LPS induced severe pathological changes, suggesting that the endometritis mouse model was well established. The qPCR assay indicated that miR-19a expression in the uterine tissues of mice with endometritis and in bEECs with LPS stimulation was significantly reduced. The overexpression of miR-19a significantly decreased the expression of inflammatory cytokines (TNF-α, IL-6 and IL-1β) and the phosphorylation of NF-κB p65 and IκBα. Similar results were also obtained following the knockdown of TBK1. Furthermore, a dual luciferase reporter assay further validated that miR-19a inhibited TBK1 expression by binding directly to the 3'-UTR of TBK1.

CONCLUSION

We demonstrated that miR-19a has anti-inflammatory effects and mediates the negative regulation of the NF-κB Pathway in LPS-induced endometritis by targeting TBK1.